The extreme Ofpe star HDE 269858 = Radcliffe 127 in the Large Magellanic Cloud (Walborn 1977), which has ejected nitrogen-rich material (Walborn 1982), was observed to be in a state of outburst on December 20, 1982. Spectroscopic observations at 2.5Å resolution with the Cerro Tololo Inter-American Observatory 1.5 meter SIT vidicon system showed a blue magnitude of 10.2, more than 1 magnitude brighter than previously, and a qualitatively changed spectrum. The Of emission features and the strong He I P Cygni profiles (especially λλ3889 and 4471) had disappeared, while the hydrogen Balmer emission remained very intense. IUE observations by S. Shore and N. Sanduleak provide evidence that the star has been in this “high” state since at least March 1981. Hence, a phenomenon related to those of P Cygni and/or Eta Carinae may be indicated. A current preprint by 0. Stahl, B. Wolf, G. Klare, A. Cassatella, J. Krautter, P. Persi, and M. Ferrari-Toniolo announces the prior discovery of the outburst at the European Southern Observatory in January 1982 and discusses extensive observations of its development, making a convincing case for interpretation of HDE 269858 as the hottest known Hubble-Sandage variable and a prime candidate for an 0 star becoming a WR via episodic enhanced mass loss.

The best X-ray position (Einstein Observatory HRI - Giacconi et al 1979) for LMC X-3 confirms its identification with the early type star first suggested by Warren and Penfold (1975). Our spectroscopic observations obtained with the CTIO 4–m telescope show the WP star is a slightly reddened B3 V star with mV ≈ 16.9. Large radial velocity variations (Δv ≈ 500 km s−1) reveal an orbital period of 1.7049 days. From the orbital elements (Table 1) one can determine the mass function f(M) = (Mx sin i)3/(Mopt + Mx)2 = 2.3 M⊙, which shows without any assumptions about the mass of the optical star, the orbital inclination, or the mass ratio the unseen X-ray object has a mass >2.3 M⊙. Detailed analysis of the HEAO–1 scanning modulation collimator X-ray data shows that the system does not eclipse, implying that the orbital inclination is ≤ 65°. Assuming the B star mass lies between 4 and 8 M⊙ (an average mass for a normal B3 V star would be about 6–7 M⊙), the mass of the unseen companion must lie between 7 and 13 M⊙ (see Fig. 4a - Hutchings, this volume). Smaller inclinations of course give even higher masses. An important point is that the unseen star must have a mass larger than that of the B star, and thus if it were any kind of normal star it should be easily seen in the spectrum. Thus the X-ray emitting object is a very good candidate for a black hole.

The supergiant H II region 30 Doradus is placed in context as the optically most spectacular component in a much larger region of recent and current star formation in the Large Magellanic Cloud, as shown by deep Hα photographs and the new IRAS results. The current state of knowledge concerning the concentrated central cluster in 30 Dor is summarized. Spectroscopic information exists for only 24 of the brightest members, most of which are WR stars; however, photometry shows over 100 probable members earlier than BO. The spectral classification of these stars is a difficult observational problem currently being addressed; in the meantime their hypothetical ionizing luminosity is calculated from the photometry and compared with that suggested for the superluminous central object R136a alone, and with the H II region luminosity. With reference to related regions in the Galaxy, the likelihood that many of the brightest objects in 30 Dor are multiple systems is emphasized. An interpretation of R136a as a system containing a few very massive stars (as opposed to a single supermassive object) is in good accord with the observations, including the visual micrometer results. The study of 30 Dor and its central cluster is vital for an understanding of the numerous apparently similar regions now being discovered in more distant galaxies.

The properties of ultraviolet interstellar extinction in and near the core of the 30 Doradus Nebula are studied. The pair method is employed using nine reddened stars from within 5′ (80pc) of the core and nine unreddened stars from a variety of locations in the large Magellanic Cloud. All of the 30 Doradus stars examined appear to be reddened by E(B-V) ⋍ 0.12 with an extinction law similar in wavelength dependence to those derived for the LMC by Koornneef and Code (1981) and Nandy et al. (1981). Several of the stars, including R136a, R145 and R147, are found to be additionally reddened by E(B-V) ⋍ 0.18 with an extinction law qualitatively similar in wavelength dependence to the law found in the Orion region. A two-component model, featuring a layer of “LMC foreground dust” which affects all of the stars and a deeper layer of “nebular dust” which affects some of the stars, provides the simplest explanation of the extinction properties. The 2200 Å extinction bump is present in both curves. The wavelength positions of the bump and the bump profiles, when normalized to a linear “background extinction”, are indistinguishable from the average Galactic bump. The strengths of the bumps, relative to E(B-V), are 20–30% weaker than for the Milky Way Curve.

The massive H II region NGC 3603 is the closest galactic counterpart to the giant LMC nebula 30 Dor. Walborn (1973) first compared the ionizing OB/WR clusters of the two H II regions and suggested that R 136, the unresolved luminous WR + 0 type central object of 30 Dor, might be a multiple system like the core region of NGC 3603. Suggestions that the dominant component of R 136, i.e. R 136A, might be either a single or a very few supermassive and superluminous stars (Schmidt-Kaler and Feitzinger 1982, Savage et al. 1983) have recently been disputed by Moffat and Seggewiss (1983) and Melnick (1983), who have presented spectroscopic and photometric evidence to support the hypothesis of an unresolved cluster of stars. We have extended Walborn's original comparison of the apparent morphology of the two clusters by digital treatment of the images to simulate how the galactic cluster would look like if it were located in the LMC

R136 is the luminous central object of the 30 Doradus nebula in the LMC. Its bluest and brightest component R136a has been interpreted as a supermassive star with a mass of approximately 2000 M⊙, based on its unusual UV spectral properties and the assumption that it is responsible for most of the ionization of the 30 Dor nebula (Feitzinger et al. 1980; Cassinelli et al. 1981; Savage et al. 1983). On the other hand, R136a has also been argued to be the core of a dense cluster, since the integrated light distribution from 0.2 to 22 pc radius centered on R136a is similar to that of a globular cluster (Moffat and Seggewiss 1983), and its optical spectrum can be synthesized by its nearby early-type stars (Melnick 1983).

R136 = HD 38268 is the luminous and diffuse central object (V ~ 10m in a region of 7 arc sec diameter) of the young populous cluster NGC 2070 at the centre of the giant H II region 30 Doradus.

It was some twenty years ago, at the previous IAU symposium devoted to the Magellanic Clouds, that Mathewson and Healey (1964) announced the discovery of the first supernova remnant (SNR) in the LMC. The method used was to identify a non-thermal radio source with a filamentary optical emission object and this confirmed N49 in the catalogue of Henize (1956) as an SNR and suggested N63 and N132 D as likely candidates.

Continuum radio emission from the Large Magellanic Cloud was first detected just 30 years ago (Mills & Little, 1953). Subsequently, surveys of the Clouds were made after each new advance in southern hemisphere instrumentation and the principal surveys are listed and briefly described in Table I. They cover a range of frequencies from 19.7 MHz to 8.4 GHz. The early surveys at low frequencies were chiefly concerned with the overall synchrotron emission from the Clouds but, as resolution improved, emphasis has shifted to the individual sources, both emission nebulae and supernova remnants, which can be recognized as Cloud members. Of recent years the unique position of the Clouds for studying radio sources in external galaxies has been undermined by the development of powerful synthesis telescopes in the northern hemisphere; these have provided equivalent sensitivity and better spatial resolution on M31, and several other northern galaxies can also be studied effectively. However, with the commissioning of the Molonglo Observatory Synthesis Telescope (MOST) in 1981 the Clouds have been restored to their rightful place befitting the closest galaxies.

The proximity, well-determined distance, and low foreground obscuration of the Magellanic Clouds makes them an ideal target for the study of galactic X-ray source populations. Steady progress since the initial detection of X-rays from the LMC in 1968 culminated in the recent Einstein Observatory surveys from which over three dozen supernova remnants and ~10 compact binaries have been identified. In this review, we record the 15-year history of Magellanic Cloud X-ray research, summarize our current knowledge, and offer a brief prospectus of what the next 15 years may hold.

In the Magellanic Clouds, about 75 candidate stellar X-ray sources have been detected. Most of these positions have now been investigated and optical identifications made for ~ 50%. The majority of sources are foreground dwarf stars or background active galaxies. Detailed investigations exist for 3 SMC sources and 6 LMC sources. It is possible to make a preliminary comparison with the population of galactic X-ray sources. The Magellanic Cloud X-ray binaries have a number of unique or remarkable properties and the most important ones are presented and discussed. These include the most rapid pulsars (SMC X-1, 0538–66), the possible precessing disk in LMC X-4, and the black hole candidates LMC X-3, LMC X-1. The properties of these objects relate to the evolution of stars in the Magellanic Clouds and how it differs from the Galaxy.

High-frequency radio continuum observations of a small sample of irregular and dwarf galaxies (Klein et al., 1983) have revealed that their integrated radio continuum spectra tend to be significantly flatter than those found for normal spirals (Gioia et al., 1982). This indicates a higher relative amount of thermal (free-free) emission.

A catalog of supernova remnants (SNRs) observed in the soft X-ray band 0.15–4.5 KeV by the imaging instruments on board the Einstein Observatory has been recently published by Mathewson et al. (1983). One of the conclusions in their paper is that SNRs in the LMC appear to evolve to large diameters much faster than predicted by the adiabatic expansion theory (Sedov 1959). This is based on the observed cumulative number-radius (N-R) relation that for the remnants in the LMC turns out to be approximatively linear. As suggested by Mathewson et al. (1983), a linear N-R relation can be obtained assuming a population of SNRs in the free-expansion phase (phase I, Woltjer 1972) expanding in a homogeneous medium. In the following we show that the X-ray surface brightness as a function of linear radius (Σ-R diagram) and the N-R relation can be alternatively explained assuming that the SNRs in the LMC are in the adiabatic phase.

In addition to the bright sources LMC X-1–X-4 and A0538–66 fifteen EINSTEIN X-ray sources in the field of the LMC appear to be non-extended and have been accurately positioned with the HRI to make optical follow-up studies feasible. At least twelve of these are not associated with the LMC, including one Seyfert galaxy at redshift 0.076 and eleven late-type galactic foreground stars, some showing photometric variability typical for RS CVn and BY Dra stars.

The sources 1E 0524.5–7013 and 0543.8–6823 are identified with variable faint blue stellar objects, the latter has been observed to exhibit variable He II and Balmer emission lines being reminiscent of the low mass X-ray binary LMC X-2. The optical counterpart of LMC X-1 is a highly reddened (V=14.5, E(B-V)=0.61) 0 7–9 type giant with variable He II and N III emission. The IPC source 1E 0501.6–7037 is probably associated with the LMC OB emission line star SK-70 36 which shows ellipsoidal light variations with a period of 6.94 days.

Further possible identifications of IPC sources with stellar objects and globular clusters in the LMC are discussed. The results indicate that only a small fraction of the non-extended X-ray sources are associated with the LMC and that a gap in the X-ray binary luminosity function exists between 1036 and 1038 erg/s.

A full account of this work will be published elsewhere.

A variety of studies over the last decade has shown molecular hydrogen to be a major constituent of the interstellar medium both in our Galaxy and in other spiral galaxies (Morris and Rickard, 1982). Our Galaxy contains roughly M(H2) = 4 × 109 M⊙; between R = 2 kpc and R = 10 kpc the H2 mass is one to three times that of HI; at the solar circle about 12 per cent of the total disk mass is in the form of H2; most of this mass is in the form of several thousand giant molecular cloud complexes (GMCs) with sizes d > 20 pc and masses M(H2) > 105 MO (Cohen et al, 1980; Sanders, 1981; Dame, 1983). These GMCs mainly consist of clumps with much smaller scales of order a few pc or less (e.g. Bally and Israel, 1983). Apart from their contribution to the total mass of the galactic interstellar medium, molecular clouds are also important as they are the major birthsite of massive early-type stars (see the review by Habing and Israel, 1979).

From radio observations it has been known for some time that a relatively large fraction of the total mass of the Magellanic Clouds is in the form of atomic Hydrogen. In contrast, optical photometry shows that both galaxies suffer rather little obscuration by dust, except in regions where the stellar population indicates recent star formation. However, the possibilities of discussing gas-to-dust ratios have been limited by the poor spatial resolution of the 21 cm HI-observations and uncertainties with respect to the relative location of the various components (gas, dust and stars).

The extinction properties of interstellar dust in the Large and Small Magellanic Clouds have been systematically investigated, using recent UV observations of early type Cloud members along with complementary visible data. The extinction curves differ systematically from the standard Galactic curve. The latter shows a broad absorption feature centred near 2200Å in virtually all sight lines but this is absent or only weakly present in the SMC; also the SMC extinction in the far UV is the largest known relative to EB-V. Dust in the LMC appears to be intermediate in extinction properties between the SMC and normal Galactic material. However, exceptions from the average extinction curves have been found in both Clouds.

Model computations show that the range of grain sizes and their number distribution law may not be significantly different in the Clouds and the Galaxy; the difference in extinction laws can be accounted for by varying the graphite contribution relative to silicate.

The state of our knowledge concerning the chemical composition of H II regions in the Magellanic Clouds is reviewed. New abundances derived from all modern published spectroscopy are presented. Some of the implications of the results regarding the nucleosynthesis of the elements and galactic chemical evolution are noted.

A review of the statistics, emission line intensities, central star fluxes, radial velocities and chemical compositions of PN in the MC is given. From these data a discussion is made of: a) the distance scale, b) the envelope mass, c) the comparison between the observed chemical abundances and those predicted from stellar evolution models and, d) the effect that intermediate mass stars have on the chemical evolution of the MC and our galaxy.